It is generally known that gas turbine engines, as used in association with many modern day aircraft, require adequate ventilation throughout the system of hot air and gases that are produced and contained within. Typically, gas turbine engines include a fan, a compressor, a combustor and a turbine. The serial flow combination of the compressor, the combustor and the turbine is commonly referred to as a core engine. Once air enters the core engine it is pressurized in the compressor. The pressurized air is then mixed with fuel in the combustor. This mixture is subsequently burned, which generates hot combustion gases that flow downstream to the turbine. In turn, the turbine extracts energy from the hot combustion gases to drive the compressor and fan. The excess hot combustion gases, not used by the turbine to drive the compressor and fan, are discharged from the core engine through an annular exhaust nozzle, which produces thrust that contributes in powering an associated aircraft. In addition to this thrust, a much larger amount of thrust is generated by the fan taking in ambient air, accelerating that air and discharging it from a fan exhaust nozzle. This thrust from the fan exhaust nozzle provides the majority of propulsion thrust for the aircraft.
The gas turbine engine has a nacelle, which includes a core engine cowl and an outer fan cowl. The core engine cowl provides an aerodynamically contoured cover for the core engine. This core engine cowl extends around the core engine and terminates at the downstream end thereof at the engine exhaust nozzle. Because the core engine cowl is radially spaced apart from the core engine, there is an area located therebetween. This area is generally referred to as the core compartment. The outer fan cowl surrounds the core engine cowl and the fan blades. In this configuration, a fan duct, which terminates downstream at the fan exhaust nozzle, is functionally defined by the area between the outer fan cowl and the core engine cowl.
As found in many engine designs, the core compartment contains various components and accessories such as those related to the hydraulic system. During operation of the engine, the core compartment, including the components and accessories, gets very hot. Overheating of the core compartment can create an adverse impact on the components and accessories therein. Thus, different ventilation systems have been used to keep the core compartment relatively cool during operation.
One example of such a ventilation system may include inlets from the fan duct to supply cold air to the core compartment. This air flow is passed through the core compartment to cool components and accessories and is then exhausted through an aft vent. Typically, under normal operating scenarios, the inlets and aft vent are sized to provide enough flow to achieve cooling objectives and maintain a desired pressure within the core compartment. Through the pressurization of the core compartment, thrust recovery is achieved through the exhaust of ventilation air from the core compartment, minimizing the efficiency penalty associated with cooling the core compartment.
Along with the design for normal operating conditions, the core compartment ventilation system must be designed to maintain safe operation during various failure scenarios. For instance, pressure relief doors have been used to vent a very large flow of hot air in the core compartment during failure case scenarios where an external duct ruptures. In these failure case systems, the pressure relief doors are located on the core engine cowl. The doors are normally closed and are triggered opened when the heat and pressure inside the core compartment becomes too great due to the ruptured external duct. With the doors open, the hot air that was contained inside the core compartment is released and continues downstream of the engine. Pressure relief doors are generally used in gas turbine engines that have a rigid core engine cowl. The doors are relatively heavy and add significant weight to the entire aircraft. In efforts to lighten the aircraft, the use of pressure relief doors has gradually been replaced with the use of flexible core engine cowls for venting of the core compartment during a failure case scenario.
The flexible core engine cowl provides the functional equivalent of pressure relief doors by deforming outwardly to allow venting of the hot air through the core compartment aft vent. The flexibility in the core engine cowl, however, causes an undesirable variation in the aft vent area during normal operating conditions. As the ventilation inlets are rigid, the reduced aft vent area during lower power operation, such as idle, produces less than the desired ventilation flow.
Thus, there is a need for an aft vent area of a core compartment that better regulates the venting of the core compartment during the different power operating conditions of an aircraft.